1. Field of the Invention
This invention relates to a combination of an oil-soluble zinc cyclic hydrocarbyl dithiophosphate and an alkenyl or alkyl succinimide and the use of said combination in lubricating oils employed for crankcase lubrication of internal combustion engines.
2. Description of the Prior Art
Metal dihydrocarbyl dithiophosphates are useful for a variety of purposes known in the art. The zinc hydrocarbyl dithiophosphates in particular are employed as oxidation and corrosion inhibitors in lubricating oil compositions. U.S. Pat. No. 3,089,850 teaches the preparation of metal cyclic hydrocarbyl dithiophosphates prepared by reacting a glycol with phosphorus pentasulfide followed by reaction with a basic metal compound.
There is a problem, however, with certain of the metal cyclic hydrocarbyl dithiophosphates of this reference in that they are essentially insoluble in lubricating oil formulations.
Thus, the insolubility and resulting essential nonuse of certain metal cyclic hydrocarbyl dithiophosphates is a severe drawback in the utility of these compounds in crankcase lubricants.